Identification of cells exfoliated from the rat kidney in experimental nephrotoxicity.

The finding of increased exfoliation rates of renal cells after the ingestion of mild analgesic and other drugs has raised the question of the significance of a celluria in assessing the extent or severity of renal damage. Certain cells in the urine may be readily recognized by their characteristic morphology, the question of their having originated from the renal parenchymal tissue itself being excluded. For example, squamous epithelial cells from the urinary tract, erythrocytes, polymorphonuclear leucocytes (provided that these are not degenerate), and aggregates such as casts and plaques fall into this category. However, the differentiation of, say, renal tubular cells, mononuclear leucocytes, and small transitional epithelial cells may often prove difficult and certainly time-consuming when large numbers of samples have to be examined, as in the present-day programmes for safety assessment of new drugs. A simple counterstain to assist in the differentiation of cells from other amorphous debris, especially when examining the urine collected from laboratory animals, is often used when examining fresh preparations of cells in counting chambers. For example, Balazs, Hatch, Zawidzka, and Grice (1963) used a composite eosin/methyl blue/picric acid stain described by Behre and Muhlberg (1937) and methylene blue itself is often used; Lippman (1957) described several nonspecific stains. However, such general cytological stains do not unfortunately provide a conclusive means of identification of the unfixed cells nor do they necessarily indicate their origin, and examination of the fresh unstained sediment, perhaps by phase contrast microscopy, will often provide as much information. Prescott and Brodie (1964) described a composite peroxidase stain which Prescott (1965) subsequently used in his study of tubular cell exfoliation after the administration of mild analgesics to human volunteers, and the use of this reagent has since been described by other workers (Davies and Kennedy, 1967; Davies, Kennedy, and Saluja, 1968). This stain is of value in inflammatory states as it gives a positive reaction with granulocytes. However, in the rat, all mononuclear cells, including transitional epithelial cells from the ureter and bladder and the renal tubule, give the same negative reaction. During the course of a recent study of the detection of early renal tubular damage in rats (Hardy, 1968) it was felt that there was still a need for the positive identification of cells as having issued from the renal tubules. One system thought worthy of attention was the oxidative enzyme succinic dehydrogenase (SDH). The histochermically demonstrated distribution of SDH in the rat kidney is well documented (Rutenburg, Wolman, and Seligman, 1953; Wachstein, 1955), the proximal and distal convoluted tubules and both the ascending and descending limbs of Henle being relatively rich in the enzyme.